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TUTORIAL - Size of squares required for Half Square Triangles and Quarter Square Triangles


Important Formulas for Quilting


I often hear people complain about the MATH in quilting. Why can’t it be easier? Well here are a few tips that I will pass on to you and hope they will help you out.


Half Square Triangles (HST) – To start, you need to know the FINISHED size of the HST. Sometimes the pattern will tell you this, but often they do not. Please check the tutorial on Determining Grid Size to help figure out what the finished sizes will be.

Step 1 – determine the FINISHED size of the HST.
Step 2 – add ONE FULL inch to the measurement from Step 1
Step 3 – cut your squares to the measurement from Step 2
Step 4 – make the HST (press them to the dark or appropriate side if necessary)
Step 5 – TRIM them to the FINISHED size PLUS   1/2"  (for seam allowance)

Example 1– I need TWO INCH finished half square triangles. Therefore, I cut my squares at THREE inches. Make the HST and trim to 2   1/2".

Example 2 – I need TWO and ONE HALF INCH finished half square triangles. I cut my squares at 3  1/2" inches. Make the HST and trim to 3 inches.

Hopefully you see the pattern. The math is the SAME regardless of the size – just make sure you follow the steps above.


Quarter Square Triangles (QST) – To start, you need to know the FINISHED size of the QST. Sometimes the pattern will tell you this, but often they do not.

Step 1 – determine the FINISHED size of the QST.
Step 2 – add ONE  and ONE HALF  INCH to the measurement from Step 1
Step 3 – cut your squares to the measurement from Step 2
Step 4 – make the QST  (you are adding 1  1/2" because making the QST involves TWO seams and therefore you need a bigger square to accommodate the seam allowances for those two seams)
Step 5 – TRIM them to the FINISHED size PLUS   1/2"

Example 1– I need TWO INCH finished quarter square triangles. Therefore, I cut my squares at 3  1/2"  inches. Make the QST and trim to 2   1/2".

Example 2 – I need TWO and ONE HALF INCH finished quarter square triangles. I cut my squares at 4" inches. Make the QST and trim to 3 inches.

Hopefully you see the pattern. The math is the SAME regardless of the size – just make sure you follow the steps above.

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